This application is a 371 of PCT/FR02/01124, filed on Apr. 2, 2002.
The invention concerns improvements to the methods for reloading machines for packaging under plastic films, called bundling machines, through the use of such films. More particularly, it concerns a method for the quick loading of the film, and of machines that implement this method.
Packaging products under film is a popular technique, which allows a number of products such as bottles, flasks, boxes, pots, or any other type of objects to be grouped together. This technique makes it possible to facilitate the transport of the products to the final destination where the packaging is removed. Depending on the type of products packaged, either the film is the only element of the packaging, or it is associated with other elements such as boards, trays or other elements on which the products are arranged before being placed under film.
Machines intended for producing such packages are called bundling machines. They allow each group of products to be enclosed in a section of film. To that end, they include, on the one hand, a device for feeding the groups of products to be packaged, such as a conveyor, and when appropriate a device for feeding associated elements, and on the other hand a distributor spool of film, a device for directing a first end of the film toward each group of products to be packaged, devices for placing the film around the group of products in synchronism with the advance of the film, devices for cutting the film when a section of sufficient length is obtained and devices for closing the film around the group of products.
In certain machines, the film used is of the heat shrinking type, and the closure is accomplished by securing the film in a film heat-shrinking tunnel. In other machines, the closure is accomplished by heat welding or gluing.
The device for directing a first end of the film toward the group of products to be packaged, called film injection device, comprises for example drive rollers between which the film is placed, and downstream of these rollers, in the direction of advance of the film, a gripping device. The film, drawn between the rollers, is then gripped by the gripping device which directs it towards a conveyor or a table on which the group of products is placed, and which causes the film to undergo a movement allowing it to enclose the group of products. Furthermore, when a sufficient length of film to form a section allowing the group of products to be enclosed is unwound, the film is cut so that a section of the film is completely available to package the group of products, and the rest of the film can be used to package the subsequent groups of products by repeating the above-mentioned operations.
Generally, and most particularly in the applicant's machines, the cutting means are associated with the injection device. In fact, said injection device comprises a first set of two rollers, called upstream, that are in tangential contact with each other, one of said rollers being the driver and the other driven, and a second set of two other rollers, called downstream, identical to the first, also in tangential contact, with a drive roller and a driven roller, and the cutting means are arranged between the two sets. The film is arranged so that it passes between the two rollers of each set, and is drawn through as a result of the pressure exerted between the two rollers of a same set. The cutting means are activated at appropriate times, in synchronism with the cycle of the machine.
These machines require that the film distribution spool be replaced regularly, when all of the available length of film has been consumed. To that end, the machines include a storage device for a full standby spool. Said standby spool is placed on this device while another distributor spool is in the process of unwinding, and the change of distributor spool requires the packaging operations to be stopped in order to heat-fuse the beginning of the film from this spool to the end of the film from the spool that is finished.
In the applicant's machines, by way of example, for the groups of products of medium size that these machines package, the change of distributor spool takes place approximately every twenty minutes, and the time of the shut-down and heat-fusing that this change involves lasts about twenty seconds if they are properly and efficiently carried out. Therefore, approximately one minute of packaging time is lost every hour because of the spool changes.
The preceding is true for films free of decorations that do not require precise positioning with respect to each other prior to the fusing. However, there are decorated films that require that the designs be aligned with the designs of the other one prior to fusing, which prolongs the operations.
In fact, contrary to what one would believe, it is not the heat-fusing of the end of the film from the full distributor spool to the end of the film from the preceding spool that consumes the most time. On the contrary, this operation makes it possible to gain time compared to the operation consisting of paying out all of the preceding film before reloading the machine with a new distributor spool. In effect, between the zone of the machine where the distributor spool is placed and the injection device, there is a compensation mechanism with a set of compensator rollers mounted on an articulated device, called “jumping jack,” which allows the tension and unwinding speed of the film to be adjusted in order to take into account the fact that the packaging operations are not carried out at a constant speed of unwinding of the film. The rollers of this mechanism cause the film to follow a trajectory that is relatively complex, and in any case non-linear, between the distributor spool and the injection device, so that if it was necessary to allow all of the film to pay out, then, at the time of reloading it would be necessary to position the new film correctly with respect to the set of compensator rollers, then engage it in the injection device by holding it correctly to prevent it from becoming crumpled or laterally offset from said injection device. These operations would take even more time to accomplish.
Thus, by heat-fusing the end of the preceding film to the beginning of the new one, the new one is immediately positioned correctly in the compensation mechanism and becomes engaged in the injection device by being drawn by the remainder of the film from the preceding roll.
However, in order for the operation to be efficiently carried out, it is still necessary for the operator to be present at the appropriate time, that is, when the end of the film is approaching.
To that end, the known machines include means of detecting the approach of the end of the film on the distributor spool that is unwinding. Said means determine the length of film remaining on this spool and are activated when it is less than a predetermined value. Indeed, because it is difficult to detect a length of film rolled onto a spool, the means often detect the remaining thickness of film on the distributor spool, which is a function of the remaining length.
These detection means can be coupled with means for warning the operator who, as soon as he is warned, takes over manual control of the machine and oversees the unwinding of the end of the distributor spool, then stops the machine at the appropriate time and performs the heat-fusing operation, restarts the machine, removes the empty spool and mounts a full standby spool. With this method of operation, if the operator is absent when the warning is given, there is a risk that the distributor spool could unwind completely and the film totally released, involving completely reloading the machine with the new film, that is, by positioning it correctly with respect to the set of compensator rollers, then by engaging it again in the injection device.
Alternatively, the detection means can be coupled with means for stopping the film. This assumes that the operator takes over manual control of the machine after the film is stopped, then oversees the unwinding of the end from the distributor spool, and stops the machine at the appropriate time to perform the heat-fusing operation, restarts the machine, removes the empty spool and mounts a full standby spool. With this mode of operation, if the operator is absent at the time of stopping, there is a risk of loss of additional time.
A purpose of the invention is to remedy these disadvantages.